The number 81520
81520 is a composite number with 20 divisors. Its prime factorisation is × 5 × 1019. Divisors (20): 1, 2, 4, 5, 8, 10, 16, 20, 40, 80, 1019, 2038, 4076, 5095, 8152, 10190 … 81520.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81520: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 16.
- 2
81520 is composite. Its prime factorisation is
- 3
The divisors add up to 189720; without 81520 itself that is 108200, so 81520 is abundant (108200 is more than 81520). Euler's totient φ(81520) = 32576 numbers up to 81520 share no factor with it.
- 4
The digits of 81520 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 76 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81520 = 2^{4} \times 5 \times 1019 \]81520 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 20 |
| Sum of divisors | 189720 |
| Euler totient φ(n) | 32576 |
| Square | 6645510400 |
| Cube | 541742007808000 |
| Square root | 285.517075 (= 4√5095) |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 76 |
| Scientific notation | 8.152 × |
81520 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand five hundred and twenty |
| Binary (base 2) | 10011111001110000 |
| Octal (base 8) | 237160 |
| Hexadecimal (base 16) | 13E70 |
| Base 3 | 11010211021 |
| As time | 81520 seconds = 22 h 38 min 40 s |
Is 81520 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81520 ÷ 2 = 40760) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (81520 ÷ 4 = 20380) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81520 ÷ 5 = 16304) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 5) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | Yes (81520 ÷ 8 = 10190) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81520 ÷ 10 = 8152) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81520 a prime number?
No. 81520 = × 5 × 1019, so it is divisible by 2.
What are the factors of 81520?
1, 2, 4, 5, 8, 10, 16, 20, 40, 80, 1019, 2038, 4076, 5095, 8152, 10190, 16304, 20380, 40760, 81520.
What is 81520 in binary?
10011111001110000 (hexadecimal 13E70, octal 237160).
What is the square root of 81520?
About 285.5171, exactly 4√5095.
Is 81520 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 81520?
81520 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 16.